More than 280,000 total hip replacement (THR) surgeries are performed in the US each year to treat degenerative joint diseases that cause pain and disability. This proposal focuses on metal-on-polyethylene prosthetic hip joints. The statistical survivorship of these implants declines dramatically after 15-20 years of use because the articulating surfaces wear excessively, and wear debris causes inflammation, osteolysis and mechanical instability of the implant. This lack of durability has unacceptable effects, such as risky revision surgery to replace a worn implant, or surgery postponement, which leaves the patient in pain and disability. While innovations such as cross-linked polyethylene (XLPE), or new materials for the femoral head have incrementally reduced polyethylene wear, no clinical studies demonstrate significant improvements of in-vivo longevity. Hence, while it may be perceived that great improvements have been made in implant design, in- vivo wear and longevity remain a significant problem that must be addressed. Our innovation to improving the longevity of prosthetic hip joints is to add a patterned microtexture composed of microsized spherical dimples to the smooth cobalt chromium (CoCr) femoral head. This is in stark contrast to existing methods or earlier research, which attempt to make smoother sliding surfaces, improve the design of the femoral head, or improve the mechanical properties of the polyethylene. Laser surface texturing is used to create a dense array of microsized concave features (dimples) on the femoral head. This patterned microtexture enhances the formation of a lubricant film and increases the separation between the articulating surfaces in relative motion and, correspondingly, reduces friction and polyethylene wear. This research will test the hypothesis that microtextured CoCr surfaces articulating with XLPE will: 1) create hydrodynamic lubrication at realistic hip joint operating conditions and thus reduce friction, and 2) substantialy reduce XLPE wear to increase longevity, and reduce revision surgeries. We will first develop a theoretical lubrication model of the microtextured femoral head and the acetabular liner. Using this model, we will optimize the patterned microtexture design to maximize the separation between the articulating surfaces and minimize friction and wear. We will experimentally validate our model and obtain a working proof-of-concept of the microtextured prosthetic hip joints, for realistic in-vivo operating conditions. We will quantitatively compare the effect of different microtexture geometries on the friction coefficient and wear rate and benchmark the results against a smooth untextured bearing surface. Showing the benefits of microtextured prosthetic hip joints will have a paradigm-changing impact because by addressing prosthetic joint longevity, both patient care improvement and health care cost reduction are addressed. In addition, this technology enables design of custom implant microtextures for e.g. low and high-activity patients.